The present invention relates to apparatus for transferring samples of a biological liquid, such as a fluid containing DNA, between laboratory appliances; and more particularly to such apparatus for transferring the biological liquid from a preparation tray to an electrophoresis apparatus.
Zone electrophoresis is a well known technique for analyzing various types of biological samples, such as blood, urine or DNA. The prepared biological samples are deposited onto a gel medium, cellulose acetate for example, which then is subjected to an electric field. The action of the electric field causes the proteins, which are amphoteric molecules, to ionize and linearly separate according to their respective electrical charge intensities. This provides a pattern in the gel which identifies constituents of the biological sample.
The process commences by preparing each of the samples in a tray containing a plurality of wells organized into a two dimensional matrix of rows and columns, such as the collection tray described in U.S. Pat. No. 5,603,899, which description is incorporated herein by reference. Each well may either contain a different biological sample to be analyzed or similar samples which are processed differently.
Various devices have been developed to transfer the biological samples from the wells. Examples of these devices are shown in the 3,616,387; 4,096,825; and 5,464,515 U.S. Pat. Nos. These transfer devices have a plurality of bibulous fingers which coincide in number and spacing with a row or column of wells within the preparation tray. The transfer is performed by dipping the fingers into a row or column of wells the absorbent material of the fingers pick up samples of the biological fluids. The transfer device then can be removed from the wells and repositioned with the fingers in contact with the electrophersis gel, thereby depositing the biological material at different positions onto the gel.
The separation of each sample's constituents occurs along a line between the electric poles of the electrophoresis apparatus. Automatic equipment has been developed which, in addition to separating biological samples by electrophoretic action, has linear arrays of photodetectors aligned with each separation line to detect the position of constituents along those lines. Thus, one set of photodetectors determines the distribution of the constituent material of one biological sample deposited in the gel.
Unfortunately, the spacing of the wells in commonly available processing trays does not coincide with the spacing of the linear photodetector arrays in standard electrophoresis equipment. Typically the linear photodetector arrays are more closely spaced than the tray wells, in order to maximize the number of samples processed during each operation of the electrophoresis apparatus. As a result, the fingers of the transfer device, which are spaced according to the well arrangement in the preparation tray, are not properly spaced with respect to the areas on the electrophoretic gel in which the deposits are to be made. The only solution is to utilize preparation trays with wells matched with the spacing of the photodetector arrays in the electrophoretic apparatus. However, such non-standard trays are often more expensive and may not be compatible with other devices used in preparing the biological samples. Further, if a laboratory has several types of electrophoretic equipment, different trays may have to be provided for each type.
Therefore, it is desirable to provide a transfer device which can accommodate the different spacing requirements of a variety of laboratory appliances.